The refuse in landfills decomposes to produce a landfill gas which may include, for example, about fifty percent methane. To recover the landfill gas, and hence the methane, wells are set in the landfill and are lined with a slotted casing. The landfill gas passes through the slots into the interior of the well and is extracted from the well for use.
One problem with landfill gas wells is that landfills typically contain an essentially liquid component or leachate which seeps into the well casing through the slots. As the leachate level rises in the well, it progressively closes off the slots, and so the landfill gas output from the well is correspondingly reduced.